Control of mine roof support assemblies

ABSTRACT

A hydraulic system for controlling the advance of a series of self advancing, powered mine roof supports of the type each having at least one double acting advancing ram arranged generally horizontally, and at least two roof supporting chock legs arranged substantially vertically, and each connected to an armored face conveyor, the system comprises one or more fluid pressure lines and one or more fluid exhaust lines connected to each support, a pilot pressure line, and a &#39;&#39;&#39;&#39;pull&#39;&#39;&#39;&#39; conduit and a &#39;&#39;&#39;&#39;push&#39;&#39;&#39;&#39; conduit connected to each support and to said pilot pressure line whereby supply of fluid along the &#39;&#39;&#39;&#39;pull&#39;&#39;&#39;&#39; conduit causes the advance of that support relative to the conveyor, and whereby supply of fluid along the &#39;&#39;&#39;&#39;push&#39;&#39;&#39;&#39; conduit causes the advance of conveyor relative to the supports. A hold circuit is provided for actuation during the advancing operation to trap fluid in the ram of each support not being advanced to hold the conveyor in place to assure forward movement of the then advancing support.

States Patent llnite j [72] Inventor Lewis 11. Bower Sheffield, England [21] Appl. No. 800,663

[22] Filed Feb. 19, 1969 [45] Patented Aug. 31; 11971 [73] Assignee A. G. Wild 8: (30., Limited [54] ONT1RO1L 01F MllNlE 110011 SUPPORT ASSEMBLIES 6 Claims, 10 Drawing lFigs.

Primary ExaminerDennis L. Taylor AttorneyLowe and King ABSTRACT: A hydraulic system for controlling the advance of a series of self advancing, powered mine roof supports of the type each having at least one double acting advancing ram arranged generally horizontally, and at least two roof supporting chock legs arranged substantially vertically, and each connected to an armored face conveyor, the system comprises one or more fluid pressure lines and one or more fluid exhaust lines connected to each support, a pilot pressure line, and a pull conduit and a push conduit connected to each support and to said pilot pressure line whereby supply of fluid along the pull" conduit causes the advance of that support relative to the conveyor, and whereby supply of fluid along the push" conduit causes the advance of conveyor relative to thc'supports. A hold circuit is provided for actuation during the ad vaneing operation to trup fluid in the rum of each support not being advanced lo hold the conveyor in place to assure forward movement 01' the then advancing support.

PATENIEB was! an WMIFB N vN Wm w HQ--- lNVE N TOP, 8 15/105 F. 80/4 58 Y fi 7 PATENTEU AUB31 1911 m mwwvww ivm mmmmm W Arrow/Em CONTROL OF MINE ROOF SUPPORT ASSEMBLIES This invention relates to a hydraulic system for controlling the advance of a series of self-advancing, powered mine roof supports, which are used e.g. when mining by the longwall system. For simplicity coal mining will be described herein, but it will be appreciated that the invention is applicable to the mining of any mineral in which similar principles are employed.

For longwall mining, it has been proposed to control electrically the advance of one support which after completing its advance signals and adjacent support to commence advancing, and so on down the whole coal face.

It is an object of the present invention to provide a hydraulic control system for operating supports in this manner.

One modification of this manner of operation is termed block or group control and the present invention is equally applicable to this modification, which consists of dividing the roof supports on the face into groups of e.g. six supports.

When it is required to advance the conveyor oneor more blocks at a time are put into push condition i.e. to push the conveyor forward, and then at the completion of the conveyor advance, one block is put into pull" condition i.e. to pull the supports up to the advanced conveyor, when the first support in that block automatically lowers away from the roof, pulls itself up to the conveyor, and upon completion of its own advance resets to the roof. On the attainment of a satisfactory setting pressure within the chocks of that roof support, the next or second support in the block is signalled to carry out the same cycle of operations as the first support and then signal the next or third support and so on to the end of the block.

Although a push operation has been described as the first operation, it is of course the obvious alternative i.e. the first operation is a pull operation to pull the roof supports up to the conveyor, followed, after resetting to the roof, by advancing the conveyor by putting the supports into push" condition.

According to the present invention a hydraulic system for controlling the advance of a series of self-advancing, powered mine roof supports each having at least one double-acting advancing ram arranged generally horizontally, and at least two roof supporting chock legs arranged substantially vertically, and each connected to an armored face conveyor, the system comprises one or more fluid pressure lines and one or more fluid exhaust lines connected to each of the supports and a pilot pressure line connected to each support via a pull conduit, a push" conduit, whereby supply of fluid along the pull conduit causes the advance of that support relative to the conveyor, whereby supply of fluid along the push conduit causes the advance of the conveyor relative to the supports, and a hold pilot line is connected to each support in such a way that the application of pressure thereto causes fluid to be trapped in the push sides of all the double-acting advancing rams by closing both the inlet and outlet valves to prevent the conveyor being drawn away from the face during the advance of the supports.

Also, each support preferably has a hydraulic circuit including a sequence valve which allows pressure fluid to pass to the next support in a sequence thereof after the first-mentioned support has been reset to the roof.

Also, each support preferably has a trip valve associated with each double-acting ram thereof, the trip valve allowing pressure fluid to pass from the pull conduit to valves causing the chocks to be set to the roof only when the ram trip valve registers retraction of the ram corresponding to the desired advance of the support. Advantageously, the trip valve is of the self-latching type.

In one preferred embodiment of the invention, a further feature relating to the pilot pressure circuit including the hold" pilot line may be included. This is of utility in certain applications of the invention to trap fluid on the push" sides of all the advancing rams, except the ra1m(s) of the support that is advancing, thereby preventing the conveyor being drawn back as a support is being advanced up to it, the hold" signal being automatically cancelled as the pull signal is given to sueceeding supports of the block.

The invention will now be described, in greater detail, by way of examples illustrated in the accompanying drawings, in which:

FIG. ll shows diagrammatically part of a first embodiment of a hydraulic system for controlling adjacent blocks of supports and illustrates one arrangement of a block of roof supports in relation to the pilot pressure line;

FIG. la shows a modification of FIG. 1 in which a hold pilot conduit and a pull-hold pilot valve are included;

FIG. 2 shows the hydraulic circuit associated with each roof support in such a block;

FIG. 3 corresponds to FIG. 1 and illustrates a second embodiment;

FIG. 4 is a hydraulic circuit diagram for a single roof support of a system for use on a unidirectional shearer face, i.e. a longwall face worked by cutting; on one direction by a machine of the well-known shearer drum type;

FIG. 5 is a hydraulic circuit for two adjacent blocks of supports on a unidirectional shearer face, the circuit of each support being as in FIG. 4;

FIG. 6 is a hydraulic circuit diagram for a single support on a bidirectional shearer face, i.e. a longwall mineral face worked by cutting in each direction of travel by a machine of the well-known shearer type; it should be noted that this circuit and the sequence of operations is the same as with reference to FIG-4 except that a combined check valve is included;

FIG. 7 shows a hydraulic circuit for two adjacent blocks of six supports on a bidirectional shearer face, the circuit of each individual support being as shown in FIG. 6;

FIG. 8 shows a hydraulic circuit of a single support on a low pressure plowing face, this system does not include a hold pilot line; and

FIG. 9 shows a hydraulic circuit for two adjacent blocks of five supports, the circuit for each individual support being as shown in FIG. 8.

Referring firstly to FIG. 1, a first block A is formed by six powered supports identified as IA to 6A, while a second six supports 18 to 6B form a block B and a third six supports lC to 6C form a block C. A common pilot pressure line 14 connects all the blocks, which are arranged along the coal face to be worked. Two short pilot pressure lines 7A, 3A are led off from the line 14, the conduits 7A, 8A pass through each block A, B, C etc. and terminating at the last support in each block,

7 which is respectively, support 6A etc. and support llA etc. The

conduit 7A is the push" conduit and the conduit SA is the pull conduit.

The conduits 7A, 8A etc. are connected in parallel to their supports and are controlled, respectively by manual valves 15A and 16A etc.

With the opening, by the operator, of the push pilot valve 15A on the block A all of the double-acting rams in that block are put into push condition, i.e., they are caused to extend thus advancing the face conveyor (not shown). The operator then moves through the supports to block B and there opens the push pilot valve 15B to cause the supports of block B to advance the conveyor in front of block B, and to complete ad vance of the conveyor in front of block A. The operator then opens the pull pilot valve 16A which allows support 1A in block A to lower from the roof and advance to the conveyor. When the advanced position is reached a trip valve (not shown in FIG. 1) is operated by the double-acting ram of the support, which allows pressure fluid to be directed to urge the chocks of the roof support to the mine roof. As soon as the pressure within the checks reaches a predetermined figure, a sequence valve (not shown in FIG. 1) automatically opens and allows pull" pilot pressure fluid to reach the support 2A in the block A and so initiate the same sequence of operations on that support, and so on to the end of block A. Blocks B, C etc. are advanced similarly.

The inventive modification of the foregoing system to include a hold" conduit as mentioned above, is described with reference to FIG. la.

Again, in this Figure, three adjacent blocks A, B and C are illustrated. A hold conduit 8'A is constituted by an extension of the pull pilot conduit 8A. This passes to the supports of the block in the reverse order to that in which they advance.

However, the hold conduit can be an independent line if required. Operation of the system of FIG. la would be effected as follows.

With the operation of push pilot valve 15A on the lock A all the push rams on that block are put into "push condition i.e. caused to extend, thus advancing the conveyor. The operator then passes through the supports whilst the rams of the supports are advancing the conveyor. By the time the operator has reached the other end of the first block, the rams will have finished pushing and he will operate an exhaust valve (not shown) to exhaust the push conduit 7A. At the same time operating push pilot valve 158 on block B causing all the rams to extend and advance the conveyor in front of block B and to complete the advance of the conveyor in front of block A.

Then operation of the pilot valve 16A on the block A, which is now a pull-hold pilot valve puts all the rams of the block A into hold and then signals the first support 1A of the block A to commence its advancing sequence.

All the various pilot control valves are incorporated into master stations, one station being positioned at each end of each block. The number and type of valve in each station is dependent on the type of mineral cutting machine that is being used and on the direction in which the machine travels.

The circuit associated with each roof support is shown in FIG. 2 which illustrates a self-advancing roof support, including floor contacting members 10, hydraulic chocks 11, a roof contacting bar 12 and one double-acting advancing ram 13 connected to work means or conveyor C and a control assembly for the support, formed by a valve block consisting of three basic elements which are a control unit 25 with servo valves 1-8, a multipiston block 17, and a cam box 26, which elements, in practice are clamped together, but which for the purpose of illustration are shown spaced apart. When clamped together, the servo valves 1 to 8 in the block 25 are axially aligned with servo cylinder assemblies 1' to 8' in turn aligned with the operating faces of the cam in the cam box 26. The valves 1 and 2 control respectively the inlet to, and exhaust from, the front chock 11, while the valves 7 and8 similarly control the rear chock 11. The valves 3 and 4 control, respectively, the inlet to, and exhaust from, the push" side of the ram 13, while the valves 5 and 6 similarly control the pull" side of the ram 13.

For clarity the ram 13 has been redrawn separately from the support unit, in order that a ram trip valve 130 may be seen. The pilot pressure line 14 is shown terminated by manual push pilot valve 15A and pull pilot valve 16A. The construction of each of the servo or poppet valves 1 to 3, 5, 7 and 8 can be seen by reference to the valve 1 in control unit 25.

Servo or poppet valves 4 and 6 are constructed as seen in the sectional view of valves 4. Valves 4 and 6 are in their normally open condition when the roof support is in its neutral conditron.

When the push pilot valve 15A is opened pressure fluid is admitted along conduit or operating means 7A to the bottom of servo cylinder and piston assemblies 3' and 4' in the multipiston block 17 via connections 14b and 14c. Piston assemblies 1' to 8' are identical and reference to the sectional assembly 1' shows their construction. They each comprise a body 18 containing a piston 19 slidably mounted within the body 18, so providing two variable volume chambers 20 and 21, one each side of the major diameter of the piston 19 with a first spindle 19a and a second spindle 19b. The minimum volumes of each of the two pressure chambers are controlled by stops on the piston 19. Fluid seals are provided at 22, 23 and 24. A valve block 25 containing valves 1 to 8 is provided in juxtaposition with the multipiston block 17.

Each poppet valve includes a valve body 27 with fluid seals 28, 29 and a valve seat 30. A valve spindle 26 slidably mounted within valve body 27 has a conical portion 26A to cooperate with the valve seat 30.

In valves 1 to 3, 5, 7 and 8 spring 31 biases each valve spindle 26 into the closed position and into the open position in the valves 4 and 6. It will be apparent that the main or mains pressure line 32 is in permanent connection with the bottom of the valves 1, 3, 5 and 7 in control unit 25, and the mains exhaust line 33 is in permanent connection with the bottom of the valves 2, 4, 6 and 8. Therefore, when the push pilot valve 15A is opened and pressure admitted to the bottom of piston assemblies 3 and 4', the upward movement of the piston in piston assembly 3 acts to lift the valve spindle of the valve 3, thus opening valve 3 and allowing pressure to be transmitted from the mains 32, through valve 3, and into line 34 to fill the push side of the ram 13. At the same time the closing of valve 4 by the piston assembly 4 prevents fluid passing to exhaust via line 48 but since the valve 6 is open this allows the fluid from the pull side of the ram 13 to be expelled across the top of the valve 5, through connection 35, through the valve 6, and into the exhaust mains via connection 36. The push pilot line 7A is in direct connection with all the supports in its block and therefore, all the rams in the block will begin to extend to advance the face conveyor C.

When advance of the conveyor in front of block A is completed i.e. by opening valve 15B in block B (FIG. 1) then the rarns of the supports of block A can be put into pull condition, i.e. caused to retract. This is achieved by opening valve 16A, which admits pressure to conduit or operating means 8A and line 38. The fluid in line 38 is transmitted to a ram trip valve with a valve spindle 13b having a valve member 132 to cooperate with a valve seat 130. However, the fluid admitted to line 8A is transmitted via connections 39, 40, 41 and 42 to the bottom of piston assemblies 2, 5', 6' and 8' respectively; and via connections 43 and 44 to the top of piston assemblies 3 and 4 respectively. As the effective area of the top of each piston 19 is greater than the effective area of' the bottom, the result of energizing the pull pilot line is to move pistons 3 and 4 downwardly, even if push pilot line is still energizing, and to move pistons 2', 5', 6' and 8' upwardly. Thus the valve 3 is allowed to close under its spring bias to cut off the fluid supply to the push" side of the ram 13, and 4 is also allowed to open, this valve serving to control exhaust of fluid along line 34 from the push side of the ram 13. The upward movements of pistons 2 and 8' opens valves 2 and 8 thus allowing the fluid in the front and rear chocks 11 to pass, respectively through line 49, across valve 1, through connection 50, through valve 2 and into the exhaust main 33 via connection 51, and through line 52, across valve 7 and through valve 8 into the exhaust main 33. The upward movement of pistons 5' and 6' opens valve 5 and closes valve 6, thus allowing mains pressure to be transmitted from line 32 via connection 45, through the valve 5 and line 46 to the pull side of the ram 13; the fluid in the push side being exhausted via line 34, across valve 3, through connection 47, through valve 4 and through connections 48 into the exhaust main 33.

As the ram 13 completes its pull stroke the piston 13d engages spindle 13b and disengages the conical seat thereof from the seal 13c. Thus the pressure fluid in line 38, which has previously been urging valve spindle 131: into contact with seat 13c is now allowed to pass through trip valve 130, enter line 53, and pass to a sequence valve 54. ln this valve, the pressure assists a spring 55 in urging a spindle 56, having a piston 56a and a conical valve member 56b, onto a seat 57. Also provided are seals 58 and 59. As well, entering line 53 pressure fluid is admitted to line 60. This moves pistons 2 and 8 down and pistons 1' and 7' up. This opens valves 1 and 7 and allows valve elements 2 and 8 to close, so allowing pressure to be transmitted from mains 32 into chocks 11 via valve 1 and 7,

and lines 39 and 52. Therefore, the chocks begin to extend towards the mine roof.

It can be seen that the pressure in the chock circuit is transmitted via line 611 to the bottom of the sequence valve 54 where it acts on the lower surface of the piston 56a secured to the valve spindle 56. The valve spindle 56 of sequence valve 54 is so proportioned that the attainment of a predetermined pressure within the chocks ll causes the conical valve member 56b to leave the seat 57 and allow the pressure previously held in lines 53 and 60 to pass through sequence valve 54 and into lines 62 and 63. The pressure in line 62 is transmitted to the top of piston assemblies )1, 6' and 7 moving their respective pistons down and allowing valves 1, 5 and 7 to close and valve 6 to open. This means that all the valves in control unit 25 are again in the position shown in FIG. 2, and in this state the support unit is considered to be in neutral position. The pressure in line 63 is transmitted to the next support 2A in the block to signal it to begin the same sequence of operations, i.e. the pull pilot line @A is now energized on the support 2A ofthe block A.

If the sequence of operations was interrupted for any reason, then provided that the pilot pressure lines are opened to atmosphere, i.e. the pressure therein is released, it is possible to operate the control unit with the manually operable cam box 26, using the piston assemblies in the multipiston block 17 as transfer members to move valve spindles in the valves 1 to 3.

The arrangement of the cams in the cam box 26 is such that movement to the left of handle '70 moves cam 71 only, to open chock inlet valve I, and movement to the right of handle 70 moves cam 72 only, to open the chock exhaust valve 2. Handle 73 and cams 74 and 75 operate similarly, to control valve 7 and 8, Handle '76 and its associated cam arrangement is such that the exhaust valve 6 is open whenever push valve 3 is open and exhaust valve 4 is open whenever pull valve 5 is open.

All the valves 1 to 8 are of the hydraulically balanced type so that when both sides of the valve are pressurized there will be equal and opposite forces acting on the valve thus keeping the valve in equilibrium, i.e. no matter where the valve stops it will remain in that position. The hydraulically balanced design of the valves prevents accidental lowering of the supports due to back pressure etc., and also keeps the operating forces required to be exerted by the servo pistons, to a minimum.

A further preferable feature is that the ram trip valve associated with the advancing ram is of the self-latching type,

that is to say while the ram is extended, the pull pilot pressure and the valve biasing spring are both tending to keep the valve closed. The conical portion of the spindle is such that its cross-sectional area is large enough to produce a force sufficient to overcome the force of the biasing spring, therefore, even if the ram, for any reason, starts to extend the trip valve will remain open thus ensuring that the signal to reset the chocks to the roof is not cancelled. A further advantage of this type of trip valve is that if one is using two advancing rams per support, the ram trip valves are connected in series and, therefore, both valves must trip and remain tripped before the signal is passed on, thus ensuring that the support has advanced fully up to the conveyor before the signal is passed on.

In FIG. 2 four pairs of inlet and exhaust valves are described but it should be appreciated that the number of pairs of valves is dependent only on the functions one required the support to perform. Thus, if a movable cantilever extension was required, a fifth pair of valves would be provided, while if powered retraction from the roof was required e.g. by providing a small vertically arranged ram at each chock, then a sixth pair of valves, would be required.

It should be appreciated that FIG. 1 illustrates a very simple form of block control using every ram as a conveyor pushing ram. However, by making only every third roof support unit a pushing unit then the blocks A, B, C etc. can be lengthened, with one man operating perhaps 24 supports on either side of a control point. This possibility is illustrated in FIG. El.

In this system the only difference between the FIG. 2 type of circuit for a pushing roof support X and that of a nonpushing support Y is that for a nonpushing unit Y connections 9a and 9b are not made. Thus when the push" conduit 7A is energized the ram push valve 3 is not operated at each nonpushing support Y.

It will be appreciated that other specific arrangements than FIGS. l and 3 are possible. For example, pushing rams are not necessarily limited to being only one in three, and operation of the manual controls allow the nonpushing rams to be used as push rams should this be required.

Embodiments of the invention will now be described with reference to FIGS. 4 to 9, illustrating specific hydraulic circuits suitable for use in particular types of working currently employed in longwall mineral faces. In these Figures, like parts to those of FIG. 2 have been given like reference numerals.

The two types of coal mining that are in common use are shearing machines and plows.

Shearing operations can be carried out either unidirectionally or bidirectionally. In the former the machine travels from one end to the other end of the coal face taking a cut, but the supports are not advanced at that time. When the machine reaches the other end of the face it is stopped and then driven in the reverse direction along the face without taking a cut. It is on this return rum that the supports are advanced in the well known snaking fashion behind the machine. When operating bidirectionally coal cutting and support advance take place on both the forward and return runs of the cutting machine.

On a plowing system all the double acting advancing rams on the face are constantly pressurized so as to always keep the conveyor tightly up to the face. The pressure is usually fairly low so as not to lift the conveyor. This action of keeping the conveyor up to the face is necessary since the plow runs on the conveyor and the plow must be forced into the mineral, the reaction being taken by the face conveyor.

The advancing rams are, therefore, constantly advancing until such time as they are fully extended, whereupon the push pressure is cancelled and the supports advanced. It will be appreciated that although the plow is cutting in both directions it is only necessary to advance the supports starting from one end.

The basic circuit to advance a support is the same for each support in a block and the same for any system of cutting, only slight modification being necessary to suit the peculiarities of each cutting system.

Referring now to FIG. l, this shows a typical circuit diagram for one support on a unidirectional shearing system the support having two double-acting advancing rams. The system is shown utilizing the hold pilot line. The operation is as follows:

Pressurizing the push pilot conduit 7A causes valve 3 of the block 25 to open and valve 4 to close thus putting the rams into push. The push pilot signal is cancelled and then the hold pilot signal is applied along hold pilot conduit b'A which causes valve 3 to close and keeps valve 41 closed thus trapping fluid on the push side of the ram. The pull pilot signal is also given at the same time as the hold pilot signal so causing the conduit 8A to be pressurized and the valve 2 to be opened, valve 4 to be opened to override the hold signal only on the advancing support due to the differential pressure across the piston resulting from the larger effective area on top, valve 5 to open and valve 8 to open thus causing the chocks llll to lower and the double-acting rams UK and 113T to start to pull i.e. retract, thereby advancing the supports. The "pull" signal then carries on to a trip valve 113a): on ram IBM, in series with a trip valve may on ram 113T, where it is blocked. When both rams have fully retracted they operate the trip valves which allow the pull signal to continue to the valve block 25 where it causes valve l to open, valve 2 to close, valve 7 to open and valve it to close, thus causing the chocks to be reset to the roof.

The pull signal then carries on to a sequence valve 54 including accumulators 64, where it is again blocked. When the pressure within the chocks 11 reaches a predetermined amount then the sequence valve 54 automatically opens thus allowing the pull signal to pass onto the next support 24 and to also pass back to the valve block via line 62 and causes valves 1, and 7 to close and valve 6 to open thus putting the support in its neutral condition. Relief valves 65 for the chocks 11 are also illustrated.

FIG. 5 shows a circuit for two adjacent blocks of supports on a unidirectional shearer face, each support having a circuit as shown in FIG. 4. Block A includes five supports 1A to 5A and block B includes six illustrated supports 1B to 6B, b'ut it will be realized that any convenient number can constitute one block or the entire supports along the face can be considered as one block. Normally each block will have the same number of supports.

Associated with each block are two master stations, i.e. stations from which the operations of the block can be controlled. A push master station 66 is located at one end, and a push, pull, and hold master station 67 at the other end. Each station 66 contains a push inlet valve 68 and an exhaust valve 69 while each station 67 contains a push inlet valve and an exhaust valve 78 and a pull and hold inlet valve 79 and an exhaust valve 80. The push pilot conduit of block A is seen at 7A, the pull pilot conduit of the same block at 8A, and the hold pilot conduit at 8'A. If the machine is cutting from 'left to right as seen in FIG. 5 then the supports are advanced by an operator travelling the face in a direction from left to right operating the master stations in turn as he comes to them and vice versa. The pressure fluid lines to the front and rear chocks and to the pull side of the ram is indicated by line 46, 49, 52, while the exhaust lines are indicated by line 46', 49, 52.

FIG. 6 shows a circuit diagram for one support on a bidirectional shearing system. This circuit and the sequence of operations is exactly as that for FIG. 4 except that a combined check valve 84 is included.

If the machine is cutting from left to right then the pull signal will also be travelling from left to right into the check valve 84 (1A) and through nonreturn valves X and Y so that, respectively, the pull and hold" lines are activated. Valve Y prevents passage of fluid outwardly from the check valve 84 (1A) to connection 'A'. On completion of the advance the pull" signal can pass to the next support 2A via connection 8A of the check valve 81 (2A).

When the machine is cutting in the opposite direction i.e. right to left, then the pull signal is also transmitted from right to left by conduit 8A (R-L), which is connected to conduit A of check valve 84 (1A), the signal passing through nonreturn valves Y and Z so that, respectively, the pull" and hold lines of the valve block 25 are activated. Valve X prevents the signal from being passed to the next block.

FIG. 7 shows a circuit for one block of six supports 1A to 6A on a bidirectional shearing system, the circuits of one or more adjacent supports being identical. The hold pilot conduit is a separate line from the pull pilot conduit, in contrast to the arrangement of FIG. 5 since the pull pilot conduit 8A must be fed to each end of the block of supports. Since for bidirectional shearing, the system must be capable of being worked in either direction then a master station 82 is provided atone end of each block, and a master station 83 at the other end, both including inlet and exhaust valves for push," pull" and hold" operations identified respectively as 84 and 85, 86 and 87, and 88 and 89.

FIG. 8 shows a circuit diagram for one support on a low pressured plowing system. Again the circuit is similar to that shown in FIG. 4, but the difference is that no hold pilot conduit corresponding to 8'A in FIG. 4 is employed. Therefore no detailed description is necessary. The only other difference from the FIG. 4 arrangement is that the pull signal from the sequence valve 54 when passing back to the valve block 25, 17, 26 puts the rams back into push and the remainder of the support, i.e. the chocks, into neutral.

I push simultaneously then inlet and exhaust push control valves 90, 91 in a master station 92 are only required at each end of the face, not at each end of each block. However, inlet -an d exhaust pull" control valves 93, 94 must be supplied for each block, and since the system is unidirectional, only one pair of pull control valves per-block is required. These valves are located in a master station 95, but those for the support A at the end of the coal face are located in the master station 92.

i A unitary -multivalve block construction that may be adopted for operation by the systemsdisclosed herein is disclosed in our US. Pat. application entitled Valve Block with Spring-Loaded Valves, Ser. No. 770,534, filed Oct. 25, I968.

All the systems described in FIGS. 4 to 9 use two main pressure lines 32 and one main exhaust line 33. However, the systems may be adapted to use only one main pressure line, i.e. the chocks and both sides of rams may use the same pressure line. Two exhaust lines could alternatively or in addition be used, i.e. the chocks would exhaust into one line and the rams would exhaust into the other line.

If the sequence of operations was interrupted, for any reason, then provided that the pilot pressure lines are opened to atmosphere, i.e. pressure therein is released, it is possible to Operate the control units with manual controls. I

What I claim is:

1. In a hydraulic system for controlling the advance of a series of self advancing, hydraulically powered mine roof supports and associated work means, each support comprising extensible chock means arranged substantially vertically for supporting the roof, advancing ram means connected between said chock means and said work means, said ram means having a push side and a pull side and arranged substantially horizontally, at least one main pressure line and at least one main exhaust line and push and pull control valve means for connecting said lines to the said ram means, pilot means for operating said valve means, said pilot means including a pull conduit for effecting connection of said main pressure line to said pull side to advance said support and a push conduit for effecting connection of said main pressure line to said push side to advance said work means, means for positioning said chock means in engagement with said roof to anchor one end of said ram means during the advance of said work means, and a hold circuit including a hold conduit to operate said push valve means to trap fluid on the push side of said ram means to positively position the same against movement during advancement of the adjacent support, whereby the work means is held against movement to anchor the opposite end of said ram means and prevent movement of said work means during the advancement of said support.

2. The hydraulic system of claim 1 wherein said ram means comprises a double-acting hydraulic cylinder, said pilot means including hydraulic servo means for closing said push valve means associated with the push side of said hydraulic cylinder, and said hold conduit comprises a pressure line for actuating said servo means.

3. The hydraulic system of claim 2 wherein said servo means comprises a double-acting servo cylinder for the push valve means including an operating servo piston, the effective surface area of said servo piston on the side corresponding to the pull side being greater than on the push side, means for connecting said pull conduit to said push valve means on the pull side, said push and pull conduit comprising pressure lines, whereby said servo piston is overriden in the pull direction when said push and pull conduits are pressurized at the same time.

4. The hydraulic system of claim 2 wherein said servo means comprises a double-acting servo cylinder for the push valve means including an operating servo piston, the effective surface area of said servo piston on the side corresponding to the pull side being greater than on the hold side, means for conmeans to said exhaust line when the advancing movement has been completed.

6. The hydraulic system of claim 4 wherein said push and pull valve means comprise separate inlet and outlet valves, said sequence means including means to bias said outlet valves to the normally open position. 

1. In a hydraulic system for controlling the advance of a series of self advancing, hydraulically powered mine roof supports and associated work means, each support comprising extensible chock means arranged substantially vertically for supporting the roof, advancing ram means connected between said chock means and said work means, said ram means having a push side and a pull side and arranged substantially horizontally, at least one main pressure line and at least one main exhaust line and push and pull control valve means for connecting said lines to the said ram means, pilot means for operating said valve means, said pilot means including a pull conduit for effecting connection of said main pressure line to said pull side to advance said support and a push conduit for effecting connection of said main pressure line to said push side to advance said work means, means for positioning said chock means in engagement with said roof to anchor one end of said ram means during the advance of said work means, and a hold circuit including a hold conduit to operate said push valve means to trap fluid on the push side of said ram means to positively position the same against movement during advancement of the adjacent support, whereby the work means is held against movement to anchor the opposite end of said ram means and prevent movement of said work means during the advancement of said support.
 2. The hydraulic system of claim 1 wherein said ram means comprises a double-acting hydraulic cylinder, said pilot means including hydraulic servo means for closing said push valve means associated with the push side of said hydraulic cylinder, and said hold conduit comprises a pressure line for actuating said servo means.
 3. The hydraulic system of claim 2 wherein said servo means comprises a double-acting servo cylinder for the push valve means including an operating servo piston, the effective surface area of said servo piston on the side corresponding to the pull sIde being greater than on the push side, means for connecting said pull conduit to said push valve means on the pull side, said push and pull conduit comprising pressure lines, whereby said servo piston is overriden in the pull direction when said push and pull conduits are pressurized at the same time.
 4. The hydraulic system of claim 2 wherein said servo means comprises a double-acting servo cylinder for the push valve means including an operating servo piston, the effective surface area of said servo piston on the side corresponding to the pull side being greater than on the hold side, means for connecting said hold pressure line to said push valve means on the hold side, said push and pull conduit comprising pressure lines, whereby said servo piston is overriden in the pull direction only when said pull and hold conduits are pressurized at the same time.
 5. The hydraulic system of claim 2 wherein is provided sequence means operative to connect said push and pull valve means to said exhaust line when the advancing movement has been completed.
 6. The hydraulic system of claim 4 wherein said push and pull valve means comprise separate inlet and outlet valves, said sequence means including means to bias said outlet valves to the normally open position. 